Look back in wonder

The Duveen galleries - the imposing halls straight ahead as you enter Tate Britain from Millbank - never look better than when filled with sculpture of the kind that fills them now. It's a free show, but one on which (given the difficulty of borrowing and moving such pieces) much effort has been expended. The Return of the Gods is the poetic title, followed by the explanatory Neoclassical Sculpture in Britain.

Neoclassical, the slim catalogue reminds us, began as a term of critical abuse, and it has probably yet to lose its pejorative tinge (unlike impressionist, say, or fauve). If it is taken as meaning that nothing in the aesthetic is original, that everything has to be licensed by the ideals of ancient Greece or Rome, then critical abuse still has the upper hand. If it is thought to connote something cold and unfeeling, or conversely sentimental and sugary, then bad art is being taken as representative of the great.

The great neoclassical art has a powerful and original sense of design. John Flaxman's illustrations to Homer and Aeschylus are full of design ideas that had never been seen before on the page, rich in invention and radical abstraction. Included in the Tate show is a recent Flaxman discovery, a marble relief depicting the Adoration of the Magi, which turned up, misidentified, in a minor auction five years ago. Many people would have placed it in quite the wrong period - in the 1920s, perhaps, or even a little later, with an influence or possibly an involvement of Eric Gill. The profiles of the bowing Magi are closely, almost perfectly, aligned. This has nothing to do with the ancient world, and is more like a response to the Italian primitives. But that alone would make it unusual for its time - the late 18th century.

Another astonishing recent find, also a marble relief, is John Deare's Venus Reclining on a Sea Monster, in which the marble is carved in such fine detail it almost looks like ivory. This was brought to the sculpture curator at the Getty, in the boot of a car, by someone who had no idea what it was. Deare, a Liverpool man, was one of the great obsessives. He once persuaded a relative of an executed criminal to lend him the man's head for the night. He cut it off himself and took it to the back wash-house of another sculptor, John Cheere. He sat up till midnight making a mould of it.

According to JT Smith, a contemporary, after Deare had finished his task, "he carried the head to the sink, and while he was pumping upon it to clear the clotted hair from some bits of plaster, he had so filled the head with water and relaxed its muscles, that the jaws opened. Deare was not at all frightened at this natural consequence, but he was most seriously alarmed when an immense and fierce yard-dog, who had heard the working of the pump, commenced barking: go out he durst not, so there he remained, after putting out his light, till the workmen arrived in the morning."

This gruesome scene would have taken place, I think, near Hyde Park Corner. Smith said he saw a cast of the head the next day, and "the character was truly terrific" (ie frightening). Smith also says that Deare was "somewhat eccentric in his ideas". He thought it quite wrong to pray to God with clothes on. "He insisted that our bodies should be entirely uncovered when engaged in addressing our Maker, and he strictly followed this practice when at his devotions. This is the custom of the religious sect called the Adamiani."

Deare died in Rome after a "silly and most eccentric experiment". He had just bought a block of marble of an unusual shape, from which he thought he could carve an interesting figure. In order to be certain how to do this, he decided to make the block his bed for the night, "so that he might receive fresh hints from the visitation of dreams, well knowing how inspiring their suggestions had been to some of the greatest men of talent". This night spent on the stone gave him a chill, from which he died a few days later.

Another exhibit from the Getty collection is a powerful bust by Francis Harwood, traditionally supposed to be of a black athlete named Psyche, who was in the service of the 1st Duke of Northumberland. This is such a striking portrait that one longs to know more about Psyche: surely if he was deemed worthy of a bust, he must have left some other trace of his existence. The mystery is compounded by the suggestion that the sculptor spent his working life in Florence, where this portrait would therefore have been made (it is dated 1758). But this seems a long time after the duke made the Grand Tour.

The bust is carved in a black stone, its surface treated with some kind of varnish in order to enhance its finish. It appears to be unlike anything else the sculptor did. But it seems to me very surprising that the Getty, with all its resources, has not managed to shed any light on its meaning. Was Psyche (black servants in Britain were often given classical names) a boxer, and is he here commemorated for his prowess in the ring? Or was he a beloved servant? Was he sent out to Florence to sit for his portrait? And was he, by the way, a servant or more properly a slave?

The great international names in neoclassical sculpture are Antonio Canova (from Italy), Bertel Thorvaldsen (Denmark) and Johan Tobias Sergel (Sweden). All are represented in the show (Canova with the Three Graces), alongside their British, Irish (Christopher Hewetson) and American (Hiram Powers) counterparts. Strangely, the gallery roof has been blacked out, giving none of the natural light these mostly white marble works were expected to be seen by. Strange, too, are the heights (or depths) at which many of the pieces are displayed. There are 29 of them in all, for the most part very well chosen to represent an important period of art, somewhat disprized by modern taste.